1. Field of the Invention
The invention relates to a method for documents with a hologram and to a document with a hologram, which in particular can be used or is suitable for the large-scale production of valuable and security documents, i.e. of identity cards, travel passes and security passes, with person-dependent, individual, diffractive optical security elements, such as for example holographic portrait photographs.
2. Description of Related Art
It is known that organic swelling agents, such as for example solvents, which are brought into contact with volume holograms can increase diffraction efficiency and influence chromaticity. The diffusion of organic molecules into the volume hologram causes a swelling and thus a change in the spacing of the holographic grating planes, resulting, in particular for reflection volume holograms, in an intensification of colour (U.S. Pat. No. 5,415,950). Nevertheless, it is not possible to swell using solvents only partial portions of the hologram that represent new visible holographic information. This requires swelling agents, the diffusion properties of which can be locally varied in a targeted manner. Monomer-containing, light-curable layers meet this requirement (EP 0828203 A2, WO 95/13568).
The dry film colour tuning method by means of a colour tuning film known from DE 689 05 610 T2, WO 95/13568 is also based on this property. In this method, the colour tuning film, consisting of a monomer-containing layer with a support film, is laminated onto a photopolymer hologram, tempered and withdrawn again from the photopolymer film. As a result of the tempering process, monomer migrates into the photopolymer and causes, in this case by swelling, a colour shift over the entire area. Partial exposure can also be carried out through a mask, with subsequent tempering and the colour tuning film being withdrawn again. The partially exposed regions in this case do not swell, as the monomers in the colour tuning film polymerise and can no longer diffuse. In this way, it is possible subsequently to introduce individual information into the photopolymer. Nevertheless, it is not known to generate individual personal data, such as for example a passport photo, by means of the colour tuning method. A drawback of this is, in addition to the necessary long tempering time of 30 minutes, which the relatively stationary monomers of the dry colour tuning film require to diffuse into the hologram, the additional material costs, in conjunction with large amounts of waste which accumulate and the additional lamination and delamination process. That is to say, owing to the excessively low bond strength, the colour tuning film cannot remain on the surface of the hologram to protect the surface of the document and must therefore be delaminated again.
For the large-scale production of documents, it is known first to produce an individual volume hologram comprising, in addition to the individual data, also standard information which was copied from a hologram master, and afterwards to attach this hologram to an associated document. In this case, the volume hologram can be generated by individual laser exposure of each individual security element in a photographic material. This can take place for example using a method, such as is known from EP 0896260 A2, with which diffractive, volume holographic, individual security features are produced on a large scale by individual laser exposure of each individual security element in the photographic material which is then later applied to the document associated therewith. The correct allocation of the individualised hologram to the corresponding personal document therefore requires costly material logistics with costly data collation. A further drawback is that two different lasers have to be used to copy standard data using one laser and to expose the individualised data using the second laser.